A self‐cleaning biological filter: How appendicularians mechanically control particle adhesion and removal

Abstract

Appendicularians are ubiquitous marine grazers that use tangential filtration to collect micron and submicron prey. The food‐concentrating filter (FCF) is the primary determinant of appendicularian prey selectivity, but the precise means by which it concentrates and conveys particles to the pharyngeal filter remain poorly understood. We used high‐speed videography to examine the mechanics of the FCF of Oikopleura dioica with high resolution to better understand how filter structure, hydrodynamics, and animal behavior affect feeding selectivity. We observed that filtration occurs through the process of serial adhesion and detachment of particles, and in this respect, differs from an industrial tangential filtration system. We demonstrate how filter elasticity and the hydrodynamics of pulsatile flow caused by the kinematics of the animal's tail contribute to the filter's self‐cleaning abilities. We present experimental observations showing that smaller particles (3 μm) adhere significantly more to the filter than larger ones (10 μm), but that, overall adhesion is quite low for an array of particle sizes (3–20 μm). This study provides a mechanistic basis for predicting the effects of appendicularian grazing on particle size spectra in the upper ocean.

Diet and trophic interactions of a circumglobally significant gelatinous marine zooplankter,Dolioletta gegenbauri(Uljanin, 1884)

“…It was speculated that these dietary differences may be due to these species occupying different locations (depths) in the water column. Conley, Gemmell, Bouquet, Thompson, and Sutherland () reported that the larvacean Oikopleura dioica is able to selectively capture and retain prey based not only on size but their shape. Selective feeding has also been reported in many other gelatinous predators including scyphozoan jellyfish and ctenophores that have long been considered to be passive feeders (e.g., Marques, Chainho, Costa, Domingos, & Angélico., ; Álvarez‐Tello, López‐Martínez, & Lluch‐Cota, ; Zeman, Brodeur, Daly, & Sutherland, ).…”

“…It was speculated that these dietary differences may be due to these species occupying different locations (depths) in the water column. Conley, Gemmell, Bouquet, Thompson, and Sutherland (2018) reported that the larvacean Oikopleura dioica is able to selectively capture and retain prey based not only on size but their shape.…”

Mammoth grazers on the ocean's minuteness: a review of selective feeding using mucous meshes

“…Sinusoidal beating of the muscular tail drives flow into the house and through the food-concentrating filter, which, for Oikopleura dioica, concentrates particles through serial adhesion and detachment in coordination with the tail beating [20]. After being conveyed through the food-concentrating filter, fluid and suspended particles move through the buccal tube and into the mouth, where they are captured on the pharyngeal filter for ingestion (figure 1b).…”

“…In Oikopleurids, size-dependent selection then occurs at the food-concentrating filters on which smaller particles are more likely to remain stuck [5,20,85,86]. After conveyance through the food-concentrating filter, particles reach the pharyngeal filter, which has a left-skewed retention efficiency curve that declines below approximately 3 mm for larger species (O. vanhoeffeni) [87,88] and approximately 1-2 mm for smaller species (O. dioica and F. borealis) [89].…”

“…At least three particle rejection mechanisms exist: (i) secretion of the pharyngeal filter may cease, causing particles to exit via the spiracles [113]; (ii) the spiracles can create a flow reversal when undesirable particles contact sensory hairs on the lips, rejecting individual particles out of the mouth or buccal tube [20,82,[114][115][116]; (iii) the lower lip can cover the mouth, causing bulk particles to be rejected nonselectively via 'pipe-smoking' [113,114,117], possibly in response to satiation at high particle concentrations (greater than 20 000 cells ml…”